Qualitative and quantitative differences in the expression of class I major histocompatibility antigens have pronounced effects on immune T cell functions such as rejection of neoplastic and virus infected cells. As a model system to study heterogeneity of class I genes we have focused our attention on the murine H-2D region genes and their products. Recent studies by us and others have defined several features of D region genes that distinguish them from other class I genes. We propose here to exploit these unique features of the D region to investigate unresolved questions of the evolution and regulation of class I genes. Our immunogenetic efforts will also continue in pursuit of new wild-derived haplotypes that express novel mutations or recombinations of D region genes. However the maor thrust of this renewal application will be the use of nucleic acid techniques to study questions regarding the heterogeneity of D region genes. Methods used will include: a) Southern and Northern hybridization analyses using low copy number probes and b) cloning select genes, confirming their identity by expression and sequencing them for structural comparisons. Questions investigated will include: l) Determining the role of duplication in the haplotype disparities in the number of D region genes - this will be approached by comparing the genes of the Dq region that has been shown to encode 3 structurally-similar molecules; 2) Studying an example of apparent genetic recombination that resulted in the acquisition of a new D region gene in one of three independently derived strains carrying the Dw3 region; 3) Investigating the genomic basis of the Ld-like prototypic structure that has been found to be shared by several D region gene products, and; 4) Probing the regulation of class I genes by determining the molecular basis for the lower expression of surface Ld and by comparing mutant mouse strains and cell lines with previously found aberrancies in Ld and/or Dd expression. In summary these studies will elucidate the genetic basis of the regulation and extensive polymorphism of class I genes in the D region.